Video playback via HDMI to Ultrawide Monitor always streched


I have my iPad pro with Infuse connected via HDMI adapter to an Ultrawide monitor (3440x1440) and when I play any video via infuse to this monitor the content is always streched.
The video settings in infuse like “Zoom Mode” or “Aspect Ratio” dont have any effect on the output.

Is there any way to have a none streched output? (f.e. with 2 black bars at each side?)

Is the aspect ratio correct while browsing in Infuse, then changes when playback starts?

no while browsing in infuse it is also streched but not fullscreen (black bars left and right).
When I start a video it switches to fullscreen (without any bars left and right)

any solution?